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Navien NCB 240 flame loss (error 12)

DrZman Member Posts: 2
Hi all,

A couple times a day, and especially every early morning, I get Error 012 (flame loss) at my Navien NCB 240. I have to reset the boiler to make it work again. I have called the installer multiple times but the problem persists. Here is what I have done so far. All with installer and recommendations of Navien support hotline:

- usual maintenance with cleaning filters etc.
- replacement of ignition rod
- redid my entire chimney with brand new polypropylene exhaust and fresh air intake

The boiler was manufactured in 2013 and installed in 2014. It used to run without problems for a while and started to cause problems the last few months, although nothing was changed.

I hope to find someone who has some new ideas or who heard of a similar problem?

Thanks, I am at the point of desperation and am thinking of having to replace this brand new boiler.


  • njtommy
    njtommy Member Posts: 1,105
    edited November 2016
    Is this a natural gas unit or propane? I doubt you have to replace the unit.

    I'm assuming what you have is a combustion problem as In a full combustion test needs to be done along with setting up the gas valve pressures too. They are generally close out of the box, but depending on your gas pressures and other factors it could be off.

    Also check your flue pipes make sure you have no blockages.

    Probably wouldn't hurt to do a full cleaning as well to the unit.
  • DrZman
    DrZman Member Posts: 2
    Thanks for the input.
    Seems the only thing I have not done is a combustion or gas pressure test.
    The odd thing about the boiler is, that when starting up it modulates up and down and when watching the temperature on the display it goes up and down. I was told this is normal for this Navien but not so sure any more: I switched on the heat and opened the hot water tab and watched the boiler modulate up and down with the flame going on and off until the error code came again. Does any of this make sense to you?
  • RiderSK
    RiderSK Member Posts: 6

    I am going through the same problem. What we know at this time is the Gas pressure is good, fires up to stage one but fails going to stage two. When the switch is set to run in diagnostic mode we set one of the switches to make it run in stage two it works fine. So all we know now is the unit has a lot of problems going from stage 1 to 2.

    Navien is sending our a replacement dual Venturi, but they are just guessing.

    I will let you know how things progress.
  • RiderSK
    RiderSK Member Posts: 6
    Hi. Problem resolved! We replaced the dual Venturi gas/air mixer. It is located on the left side upper section. It is the housing that the gas and blower connect to. It has a small motor that must be bad.

    System works great now.
  • RiderSK
    RiderSK Member Posts: 6
    Hi. Just one other comment. You should have a tail on your gas line so any particles in the gas don't end up in your gas valve.
  • john p_2
    john p_2 Member Posts: 367
    Thats funny, all the utilities claim dirt leg on gas pipe are no longer needed as their gas is pure. LOL, I still install them...
  • rmb185
    rmb185 Member Posts: 1
    Just wanted to say that my unit was doing the same thing - firing up for a second, then shutting down for 3-5 seconds, firing up again for a second, then shutting down, etc. The Navien tech on the phone helped me narrow it down to the dual venturi trying to get to stage 2. They're sending me a replacement as well. Not sure if there's something going on with these parts.

    I did notice that the little window that allows you to see if the burner is firing was completely gummed up with dirt (unit is about a year old). That might indicate some sort of impurity in the gas line or something.
  • njtommy
    njtommy Member Posts: 1,105
    edited January 2017
    Could also be where your pulling combustion air in from too. For the gumming and dirty heat exchanger
    j a_2
  • anthonyk
    anthonyk Member Posts: 1
    I have a Navien 210 boiler and have been having the same issue, the flame in my boiler (3 years old) keeps shutting on and off after 13 seconds then the boiler shuts down with error code E 012 (flame loss). I called my HVAC tech and the ignitor probe was cleaned. the system ran fine for the day. The next trip to my house (2 days later - same issue) I was told there was low/no gas pressured that the propane regulator was bad or freezing. 4 days later and several system resets the propane company replaced their regulator and this seemed to work but was short lived, as the boiler kept shutting down with the same error code (flame loss). 3 days later and several more system resets I called my HVAC tech for yet another call for service. After several diagnostic tests, the HVAC tech called Navien tech support and they diagnosed the issue to be the "Dual Venturi". The part is being sent out, hopefully this will resolve my issue. For now its been unplugged and the boiler is running fine. I will post an update when the part is installed.
  • Keifer301
    Keifer301 Member Posts: 7
    I have a Navien boiler doing the same thing and the Navien tech support says everything tests out fine.
    How did the new dual venturi install work out for you?
    Loving the fact to be known as an old timer and seeing the changes I have seen.
  • Yeowza
    Yeowza Member Posts: 1
    I have a Navien NCB240 that had been running great but would periodically get an Error Code 12. I had Xcel come and measure the gas pressure and it was fine. It got worse this year to the point where I would have to reset it every hour. I found a post on another site that mentioned five screws on the top of the heat exchanger (easily accessed with the lid off. they point down to the ground). I checked the screws on mine and they were lose. I tightened them all and bingo, it has not stopped with the Error Code 12 since. I wish I had found this before trying 2 different Navien certified techs and a few calls to Navien. I plan to check the screws periodically to see if they work themselves lose. If so I will put a little locktite on them.
  • tau_
    tau_ Member Posts: 5
    Hi, to all of those that have had problems in this thread. Can you comment if it has been fixed and how? I'm having the same issue and it seems to mainly be on colder days. I have propane. I am going to call service tech but I like to learn more about the issues before going in blind. Good to have some background knowledge.